Have you seen the words high-intensity interval training online and wondered what it meant? The name gives away some of the details. High-intensity activities raise your heart rate.

According to the New York Times, "high intensity" is 80-90% of a person's aerobic capacity.

As a heart rate number, this varies by person according to age and other factors. If you have a smart watch with heart rate monitor, it will log this heightened heart rate as "intensity minutes."

But you don't have to have a heart rate monitor to do HIIT; you can also gauge it by the amount of sweat dripping down your face (it's a lot).

Another key part of high-intensity interval training is the intervals. Rather than run on a treadmill for an hour without stopping, intervals alternate periods of activity and rest.

In high-intensity interval training, the intervals tend to be 30 seconds to 60 seconds.

The idea is to go "all out" during those few seconds because resting is just around the corner. It's also easier to go "all out" knowing that the entire workout is only 15 to 20 minutes. The example workouts that I'll show later are all 20 minutes or less.

Why the recent upsurge in high-intensity interval training? A few years ago, only professional athletes were training with high-intensity intervals.

However, training programs that rely on high-intensity intervals have been wildly popular. P90X and Crossfit are two examples.

One reason that people may have adopted these workouts is that recent health studies show that many people can benefit from this type of training.

A 2014 study not only analyzed the benefits of high-intensity interval training but also suggested that people found it more enjoyable than continuous exercise (such as running on a treadmill at a steady pace).

Sounds pretty good, huh? I've outlined some of the health benefits in the next section.

Benefits of High-Intensity Interval Training

High-intensity interval training was one of the most popular workout types in 2014. It continues to grow. I've seen two Crossfit places open up in my area over the past two years.

Build Endurance for HIIT

Although long bouts of aerobic cardio like treadmills have long been touted as building endurance, these short bursts of energy can also help you endure longer workouts. A 2012 Journal of Physiology study compared two groups' endurance.

One group did high-intensity interval training, and the other did endurance training. Even though the high-intensity group did 90% less exercise, they showed some of the same benefits as the endurance group. Increased cardiovascular fitness was visible in both groups.

Breathe Easier (When It's Over)

Working out with less oxygen, called anaerobic activity, trains your body to do more with less. This increases oxygen uptake, which is an indicator of cardiovascular fitness.

Strengthen Your Heart with HIIT

All that HIIT increased oxygen benefits the heart too. The heart pounding activity can make arteries more flexible, according to a Men's Fitness expert. More flexible arteries tend to be wide enough to accommodate blood and avoid dangerous blood clots.

The New York Times reports that patients with heart disease could also tolerate high-intensity interval training better than moderate continuous exercise.

Burn More Calories (and for Longer)

One reason people love high-intensity interval training is that you keep burning calories after the workout has ended. Compared to continuous training, high-intensity interval training burns more calories during and after a workout.

Calorie burning can be increased for up to two hours after a workout. For those trying to lose weight without working out daily, high-intensity interval training could be a good choice.

Work out for Less Time

All these benefits happen within a 15 to 20-minute workout completed three times a week doing. Can you believe it?

That's one hour of working out (HIIT) per week! With the increased calorie burn, you might be able to ditch a weekly treadmill session if you start high-intensity interval training. Research backs this up.

The groups of cyclists that trained either high intensity or endurance both experienced similar benefits, but the high-intensity group only worked out for 10% of the time that the endurance group did.

Get the Benefits of Weight and Cardio Together

Many fitness gurus recommend that people do both cardio and weight training for maximum health benefits. The cardio builds endurance and strengthens your heart. The weight training builds muscle mass.

High-intensity interval training combines the two. Many of the activities are body-weight exercises, but you get the cardio benefit because you complete them quickly.

H.I.I.T. Workouts for Beginners

Beginner Workout by Moms Into Fitness

A great introduction to HIIT by the female trainer preps you for this 10-minute workout. She explains that the workout has 40 seconds of intense activity followed by 20 seconds of rest. During the intense seconds, she extols doing "as many repetitions as possible."

The HIIT warmup starts with a set of squats and knee raises. As the workout progresses, you can see how many sets are left with a countdown on the right.

The HIIT sets don't have anything surprising or scary. There are squats, push-ups, lunges and side planks. The video ends with a nice cooldown and stretching session.

Home Workout for Beginners by The Body Coach TV

The Body Coach, a male trainer with a sexy accent, introduces this longer 20-minute workout with a short warmup. The warmup includes gentle jogging and some basic stretches.

The HIIT workout has 30-second intervals, 30 seconds of activity followed by 30 seconds of rest.

Exercises include high knees, burpees, "mountain climbers" and power squats. He quickly demonstrates each before jumping into the activity.

His HIIT workout is repetitive so that you can get the hang of each exercise. There is a short cooldown at the end.

Beginner Workout by Fitness Blender

This video features a female workout guide and a male voiceover that narrates the 17-minute workout. Four minutes are devoted to a warmup up with stretches.

This workout has the shortest activity time of only 20 seconds, but it also only gives 10 seconds of rest. Exercises include jumping jacks, ski squats, and traveling push ups.

Each HIIT is repeated as a set. If these exercises are unfamiliar activities to you, that's okay. This video shows the exercise a few times before it tells you to start.

Unlike the other HIIT videos, this one doesn't have a cooldown, though.

These three videos are only a sample of the many high-intensity training videos available. P90X and Crossfit provide other alternatives too.

If you prefer to work with equipment, Crossfit may be a good alternative. I always see people tossing tires when doing Crossfit. Another advantage I didn't mention is flexibility.

The types of HIIT workouts are endless. As you get used to the concept, you can invent your own exercises and intervals.